Solitary myofibroma in adults: clinicopathological analysis of a series.

Solitary myofibroma is a recently described, benign neoplasm of superficial soft tissue, which represents the adult counterpart of infantile myofibromatosis and is poorly recognized. Eleven new cases are presented herein. The patients were mostly adults with ages ranging from 13-64 years. They presented with a solitary, usually painless nodule of variable duration in the skin or oral cavity. Histologically, each lesion had a biphasic pattern with spindle cells forming fascicular or whorled areas and rounded, more primitive cells arranged around small vessels, forming haemangiopericytoma-like areas. The characteristic zonation of infantile myofibromatosis was often less marked in adult lesions and there was a haphazard arrangement of the fascicular and pericytic areas in some cases. Hyalinization, especially of the peripheral spindle-celled areas, was frequent. Immunohistochemically, the spindle cells were desmin negative but muscle actin (HHF-35 and IA4) positive. The rounded cells were both desmin and actin negative. Electronmicroscopy confirmed the myofibroblastic/fibroblastic nature of tumour cells in two cases. Although vascular invasion was seen in two cases, solitary adult-type myofibroma pursues a benign clinical course.